Electrode and component therefor



July 13, 1965 G. A. FREEMAN ELECTRODE AND COMPONENT THEREFOR Original Filed Dec. 22, 1959 FIGQ5.

INVENTOR 650266 A. FREEM/IN FIG. H.

United States Patent 3,195,605 ELECTRGDE AND CQMPGNENT THEREFOR George A. Freeman, East Orange, NJ assignor to Westinghouse El ctric Qcrporation, East Pittsburgh, Pin, a corporation of Pennsylvania Original application Dec. 22, 1%9, Ser. No. 861,339, new Patent No. 3,132,409) dated May 12, 1964. Divided and this application Dec. 2, 1960, Ser. No. 73,386 4 Claims. (iii. 313-344) This invention relates to a thermionic electrode for an electric discharge device and, more particularly, to an improved component therefor and is a division of copendi-ng application Serial No. 861,339, filed December 22, 1959, now US. Patent No. 3,132,409.

Recently there has been marketed in this country an improved thermionic electrode for high pressure mercury vapor (HPMV) lamps that markedly increases both the useful life and lumen maintenance of such lamps by providing a reservoir of electron-emissive material that is shielded from the gaseous discharge and the erosive effect thereof. This is accomplished by depositing the emission material by means of a dip process between the spaced intermediate turn or turns of a refractory wire coil that has closed end sections and is mounted on a suitable core member such as a tungsten rod. A tightly wound outer coil is then threaded over and interlocked with the inner coil thereby enclosing the expanded medial section thereof and the reservoir of emission material therein. The emission material is thus protected from the arc and the sputtering of such material onto the bulb surface and the resultant progressive blackening thereof is inhibited.

As presently manufactured the inner coil and core member are dimensioned to be locked together by means of a force fit. However, since the inner coil must be tightly fitted onto the rod to permit the outer coil to be threaded over the inner coil and locked therewith without displacing the latter, it frequently happened that the expanded medial section of the inner coil partially collapsed and became permanently distorted as the rod was being inserted. When this occurred the inner coil had to be discarded since the spacing between turns of the expanded section thereof was decreased and said section thus could not hold or accommodate the required amount of emission material. Narrowing the diameter tolerances of the rod and inner coil as much as practical to minimize the compressive stress on the inner coil and prevent the expanded medial section from collapsing during assembly failed to solve this problem.

It is accordingly the general object of the present invention to provide a composite type electrode of the aforesaid character that will obviate the foregoing and other problems associated with the fabrication thereof.

Another and more specific object is the provision of an inner coil for such composite electrodes that is not only easier and less expensive to manufacture but which will facilitate the assembly of the electrode.

The aforesaid objects of the invention, and others which will become apparent as the description proceeds, are achieved by providing an inner coil that has a protruding end segment of such length that it can be engaged by a suitable holder, such as that disclosed and claimed in copending divisional application Serial No. 73,387, filed December 2, 1960, entitled Apparatus for Assembling Electrodes, now US. Patent No. 3,110,094. The coil can thus be held without constricting it, or obstructing access to its interior. This, in turn, permits the core rod to be concurrently rotated and conveniently inserted into the coil in the manner disclosed and claimed in the aforesaid copending parent application Serial No. 861,339.

A better understanding of the invention and the mannor 'in which the aforementioned objectives are achieved will be obtained by referring to the accompanying drawing wherein:

FIG. 1 is a side elevational view on a reduced scale of an arc tube for a HPMV lamp which incorporates the electrode coil component of this invention;

FIG. 2 is an enlarged side elevational View, partly broken away and in section, of one of the lamp electrodes;

FIG. 3 is an end view, of the arc-supporting portion of the electrode illustrated in FIG. 2;

FIGS. 4 and 5 are side elevational views of the inner coil before and after the coil legs have been trimmed, respectively, in accordance with the invention;

FIG. 6 is a side elevational view of an alternative coil embodiment;

PEG. 7 is a plan view of a preferred form of coil holder for facilitating the assembly of the coil and core rod;

FIG. 8 is a cross-sectional view of the holder taken along the line VIIIVIII of FIG. 7, in the direction of the arrows;

FIG. 9 is a plan view of the coil holder corresponding to the view shown in FIG. 7 but'with the coil illustrated in FIG. 5 inserted into the holder and locked in keyed relationship therewith;

FIG. 10 is a cross-sectional view of the holder and inserted coil taken along the line X--X of FIG. 9, in the direction of the arrows; and

FIG. 11 is a side-sectional view of the coil and holder similar to the view shown in FIG. 10 but with the core rod in its assembled position on the coil preparatory to the withdrawal of the rod-and-ooil assembly from the holder.

While the present invention can be advantageously employed in conjunction with various kind of devices wherein one member is force-fitted into another component that is susceptible to deformation when compressively stressed, it has particular utility in connection with thermionic electrodes for HPMV lamps and has accordingly been so illustrated and will be so described.

With specific reference to the form of the invention shown in the drawing, in FIG. 1 there is shown an arc tube 12 for a I-IPMV lamp comprising a tubular envelope 14 of quartz or the like that is closed at each end by a press seal 16. A pair of oppositely disposed thermionic electrodes 20 are anchored in each of the seals 16 and electricallyconnect with the usual ribbon-conductor assemblies 18 which are hermetically embedded in and extend through the aforesaid seals. A filling of ionizable starting gas such as argon or the like is also sealed within the envelope 14 along with a charge of mercury 13 and an auxiliary electrode 21 that is disposed adjacent one of the main electrodes 29 and electrically connects with a separate ribbon-conductor assembly 19.

As shown more particularly in FIGS. 2 and 3, each of the main electrodes 20 consist generally of an outer coil 24 and an inner coil 26 of linear configuration, and a core member such as a cylindrical tungsten rod 22 that is inserted into and locked by means of a force fit with the inner coil. Both the outer coil 24 and the inner coil 26 are of substantially uniform diameter and are wound from refractory metal wire such as tungsten for example. The outer coil 24 is tightly wound so as to form a closed helix and is threaded over and interlocked with the inner coil 26, the end turns whereof are also tightly wound and constitute closed end sections. The intermediate turns 28 of the inner coil 26 are spaced a predetermined distance apart and from the closed end sections thereby to provide an expanded medial section that is filled with a predetermined amount of suitable electron-emissive material 30, such as the well-known alkaline earth carbonates, thoria, etc., or mixtures thereof for example.- The emission material 36 is preferably applied by mixing it with a suitable binder to form a slurry and then dipping the rod-and-inner coil assembly therein. Upon hardening the emission material firmly adheres to and bridges the intermediate turns 28 and fills the expanded medial section of the coil as shown. The end of the rod 22 opposite the aforesaid coils is preferably shaped to provide a flat end section 21 in order to facilitate the electrical connection thereof with the ribbon-conductor assembly 18 and its subsequentembedment in the press seal 16. The aforesaid inner and outer coils are preferably located a predetermined distance inward from the cylindrical end of the core rod 22 as shown.

The present invention relates to an improved inner coil component for composite type electrodes of the aforesaid character rather than to such electrodes per se and this component will now be described.

As shown in FIG. 4, the inner coil 26 as wound has a leg 31 at each end which protrude at substantially right angles from the same side of the coil. Instead of cutting both legs 31 in a direction parallel to the longitudinal axis of the coil asheretofore to provide a so-called square cut end turn 32 such as that shown in FIG. 5, only one leg is thus processed and the other severed at a point located a predetermined distance from the coil body. Thus, at least one of the end turns of the inner coil 26 is terminated by a substantially straignt end segment 34 that protrudes laterally from the outer surface of the coil body and constitutes a tangential extension of the aforesaid end turn, as illustrated in FIGS. 2, 3 and 5. To facilitate the assembly operation and serve as a stop for the outer coil as hereinafter described, the end segment 34 is dimensioned to project beyond the outer surface of the coil a distance at least equivalent to the diameter of the wire from which the inner coil is wound and preferably about twice the wire diameter. This permits the leg 31 at the end of the coil to be cut while the coil is still on the coil winding machine thus affording the additional advantages of reducing the cost of the coil by eliminating at least one of the manual cutting operations heretofore required and the resultant burr at the entrance to the coil that necessitated, in turn, a deburring operation and the maintenance of close diameter tolerances to permit easy insertion of the rod 22.

Alternatively, instead of employing a cutting wheel to form the square cut end turn 32 the coil leg 31 can be cut in a direction normal to the longitudinal axis of the coil to provide an inner coil 26a having an end turn 32a that is tapered rather than terminated abruptly, as shown in FIG. 6. This type coil is preferred since both ends of the coil'can then be trimmed by machine instead of manually as heretofore thereby further reducing the manufacturing cost of the coil.

Assembly of the core rod 22 with the inner coil 26 is accomplished in accordance with the process claimed in the aforementioned copending parent application Serial No. 861,339 wherein the rod is concurrently rotated and inserted into the coil while the latter is held and prevented from turning or moving in an axial direction. A preferred apparatus for holding the inner coil 26 during the assembly thereof with the rod 22 in accordance with the foregoing procedure is illustrated in FIGS. 7 and 8, which apparatus is claimed in the aforesaid copending divisional application Serial No. 73,387. As shown, the holder comprises a rigid support member 36 having a major cavity 38 that extends inwardly from one end of said member and merges with a minor cavity 40 that opens into and coaxially extends from the bottom of said. major cavity. Both of the aforesaid cavities are of cylindrical configuration, the major cavity being at least as long as but slightly larger in diameter than the outside diameter of the inner coil 26, as for example .010 of an inch in the case of a 1000 watt coil that has an outside diameter of approximately .149 of an inch. The minor cavity 49 is slightly larger than the diameter of the rod 22 and has a length equal to the distance between the cylindrical end of the rod 22 and the outermost turn of the inner coil 2&5 when the latter is locked in its position of use on said rod.

Due to the difference in diameter of the aforesaid major and minor cavities there is provided an inwardly protruding annular shoulder 41 at the bottom of the major cavity'3il which is adapted by virtue of its location to serve as a stop for the inner coil 25 when the latter is placed into the holder as set forth below. A recess such as a groove 35? is provided in the face of th support member 36 which groove communicates with and extends tangentially from the major cavity 38, as shown most particularly in FIG. 7. The depth of the groove 39 is at least equivalent to the diameter of the wire from which the inner coil 26 is wound and is of sufiicient length to accommodate the uncoiled end segment 34. The minor cavity 56i may be vented to the atmosphere as by a passageway 42 that' extends from the bottom thereof to the proximate face of the support member 36. 7

Assembly of the rod 22 and inner coil 26 is accomplished by inserting the end of the coil opposite the end with the uncoiled end segment 34 into the support member 36 and turning the coil so that the aforesaid end segment falls into the groove 39. This key locks the members together and seats the coil against the annular shoulder 41 at the bottom of the major cavity 38, as shown in FIGS. 9 and 10. The core rod 22 is then concurrently rotated about its own axis and inserted into the inner coil 26 in the manner described in the aforesaid copending parent application Serial No. 861,339. This permits the rod to be inserted with a minimum amount of thrust and compression of the expanded intermediate section of the coil. When the end of the rod 22 seats against the bottom 43 of the minor cavity 46 and the inner coil 26 is thus precisely located in its position of use on the rod, rotation of the rod is stopped, the rod-and-coil assembly is withdrawn from the support member 36', and the subsequent operations required to complete the fabrication of the electrode 20 are then carried out.

It has been found that fabricating the inner coil 26 and assembling'it with the rod 22 in the foregoing manner surprisingly reduced the shrinkage due to distorted coils from about 25% and higher to less than 2%.

As will be noted in FIGS. 2 and 3, when the outer coil 24 is threaded over the inner coil 26 the innermost end turn of said outer coil is seated against the protruding end segment 34. Thus, in addition to decreasing the manufacturing cost of the inner coil and facilitating the fabrication thereof and the assembly operation, said segment also serves as a stop for the outer coil that automatically positions it in the proper location on the coil-and-rod assembly.

It will be recognized from the foregoing that the objects of the invention have been achieved by providing an improved coil component for a composite thermionic electrode which reduces the manufacturing cost of the electrode, facilitates the assembly of said coil with the electrode core member and makes this operation readily adaptable to automatic manufacturing techniques.

While several embodiments of the improved coil component have been illustrated and described, it is to be understood that various modifications can be made therein without departing from the spirit and scope of this invention.

I claim:

' 1. As an article of manufacture, an inner coil component for an electric discharge lamp electrode wherein a tightly wound outer coil is threaded over and interlocked with said inner coil component to form a composite electrode, said inner coil component comprising a length of tungsten wire wound into a helix of linear configuration having at least one intermediate turn and a pair of spaced end turns of substantially the same outside diameter as said intermediate turn, said intermediate turn comprising an expanded medial section that is wound at a ditferent pitch than the turns of said outer coil, one of said end turns being terminated by an uncoiled substantially straight end segment that protrudes laterally beyond the helix a distance at least equivalent to the diameter of said wire and constitutes a rigid stop for automatically locating the outer coil in its position of use on said helix.

2. As an article of manufacture, an inner coil component for an electric discharge lamp electrode wherein a tightly Wound outer coil is threaded over and interlocked with said inner coil component to form a composite elec trode, said inner coil component comprising a length of stiff tungsten wire wound into a helix of linear configuration having a plurality of spaced intermediate turns and a plurality of end turns of substantially the same diameter as said intermediate turns, said intermediate turns constituting an expanded medial section which defines a reservoir for electron emission material and has a larger spacing-between-turns dimension than that of said outer coil, at least the outermost ones of said end turns being tightly wound and constituting a closed end section at each end of said helix, the outermost end turn of one of said closed end sections being terminated by an uncoiled end segment that protrudes beyond said helix at substantially a right angle relative to the longitudinl axis of the helix, said uncoiled end segment projecting beyond said helix a distance at least equivalent to the diameter of the wire from which the helix is wound and constituting a rigid stop for automatically locating the outer coil in its position of use on said helix.

3. In an electrode for a high-pressure gaseous discharge lamp, the combination of; a first helical coil of refractory metal wire having (a) an intermediate turn that is spaced from the adjacent turns and defines an expanded medial section and (b) an end turn that is terminated by an uncoiled laterally protruding end segment, and a second helical coil of tightly wound refractory metal wire that is threadably interlocked in enclosing relationship with said first helical coil and is seated against the protruding end segment thereof.

4. The combination set forth in claim 3 wherein the other end turn of said first coil is terminated along a line that is substantially normal to the longitudinal axis of said first coil and is thus provided with a tapered terminus that is located Within the confines of the coil body.

References Qited by the Examiner UNITED STATES PATENTS 2,007,939 7/35 Braselton 315-1851 2,153,008 4/39 Scott 313-344 2,175,385 10/3-9 Endsley 267-9 2,241,362 5/41 Gustin et a1 313-211 X 2,479,193 8/49 Zabel 313-344 2,687,489 8/54 Anderson et a1 313-211 2,765,420 10/56 Martt 313-211 X 2,838,715 6/58 Payne BIS-108.1

DAVID J. GALVIN, Primary Examiner. RALPH G. NILSON, Examiner. 

1. AS AN ARTICLE OF MANUFACTURE, AN INNER COIL COMPONENT FOR AN ELECTRIC DISCHARGE LAMP ELECTRODE WHEREIN A TIGHTLY WOUND OUTER COIL IS THREADED OVER AND INTERLOCKED WITH SAID INNER COIL COMPONENT TO FORM A COMPOSITE ELECTRODE, SAID INNER COIL COMPONENT COMPRISING A LENGTH OF TUNGSTEN WIRE WOUND INTO A HELIX OF LINEAR CONFIGURATION HAVING AT LEAST ONE INTERMEDIATE TURN AND A PAIR OF SPACED END TURNS OF SUBSTANTIALLY THE SAME OUTSIDE DIAMETER AS SAID INTERMEDIATE TURN, SAID INTERMEDIATE TURN COMPRISING AN EXPANDED MEDIAL SECTION THAT IS WOUND AT A DIFFERENT PITCH THAN THE TURNS OF SAID OUTER COIL, ONE OF SAID END TURNS BEING TERMINATED BY AN UNCOILED SUBSTANTIALLY STRAIGHT END SEGMENT THAT PROTRUDES LATERALLY BEYOND THE HELIX A DISTANCE AT LEAST EQUIVALENT TO THE DIAMETER OF SAID WIRE AND CONSTITUTES A RIGID STOP FOR AUTOMATICALLY LOCATING THE OUTER COIL IN ITS POSITION OF USE ON SAID HELIX. 